1. Field of the Invention
This invention relates to arrangements for supporting rotatable drums such as rotary kilns, tube mills, drum sieves and the like.
2. Description of the Prior Art
Rotary drums such as rotary dryers, tube mills, drum sieves and particularly rotary kilns are commonly supported by roller supports. The rotary drums usually are provided with two or more ring-like members known as "track rings" or "live rings" which are secured to the outer circumference of the drum body. Each live ring rests upon a pair of the roller supports. These roller supports rotate about roller shafts which are mounted on solid foundations. In some cases, each roller support is composed of several rollers engaging the live ring and sharing the load of the rotary drum with its material charge.
Ideally, the outer surface of the live ring bears correctly against the outer surface of the roller supports along a common generatrix. The drum with its live rings then is correctly aligned with the support rollers in a vertical plane and along the axis of the drum. However, due to the weight of the drum with its material charge, as well as heat transferred to the drum from the hot material inside, the drum will tend to warp and/or twist. The drum and its attached live rings become temporarily or permanently misaligned (in a vertical plane and/or along the axis of the drum) with the support rollers and the live rings inaccurately bear against the support rollers, not along a common generatrix.
Under unfavorable conditions, the load on the support rollers may increase to a multiple of the normal load for which the support rollers are designed. Such loads result in localized contact pressures between the live ring and the roller supports which cause severe damage to the live rings and the support rollers. Because of the unequal distribution of the load on the support rollers, a total breakdown or collapse of the roller supports may result. Further, the unequally distributed load contacting the surface of the support rollers may inadvantageously cause edge pressure on the rollers.
To compensate for such misalignments, it is a usual practice to provide the drums with roller supports which are designed to take these conditions into account. For example, the rollers may be supported pivotally in bearings to compensate for axial misalignment, and the bearings may be resiliently supported to compensate for misalignment in the vertical plane.
It is thus well known to use a roller support in which the bearings for the roller shaft permit pivotal movement of the roller shaft and permit displacement of the roller shaft bearings in a substantially vertical plane. The bearings may be supported by a member having a surface configured as a section of a sphere. A housing for each bearing may be supported directly or indirectly by a hydraulic cylinder or a flexible cushion. More particularly, the housing may be supported on a rocker pivoting about an axis substantially parallel to the axis of the drum. As a result of the prior art arrangements, the rollers tend to follow the live ring track on the drum but inadvantageously, localized pressure still exists.
To compensate further for any misalignment, the hydraulic cylinders may be interconnected and balanced with each other by equalizing connections. The roller supports, however, must inadvantageously be fully dependent upon an auxiliary hydraulic system.
Further, the known roller bearings in which the bearings for the roller shaft are supported by flexible cushions (such as rubber pads) do not satisfactorily equalize the misaligning forces exerted by the drum on the roller bearings. That is, the live ring and roller bearings do not fully align along a common generatrix resulting in damage to the machinery.
We have invented an improved roller support arrangement for supporting rotary drums which overcomes the disadvantages of the prior art by providing improved compensation of misalignments due to warping or twisting of the drum.